This invention relates generally to cushioning devices and relates more particularly to a pneumatic spring for damping the relative motion between two objects, such as a vehicle seat and a base upon which the vehicle seat is supported.
It is known that a pneumatic spring, such as an air spring, can be utilized within a vehicle seat assembly for damping the vibrations to which the vehicle seat may be exposed. One such spring which is shown and described in U.S. Pat. No. 3,628,763 utilizes a rolling lobe type of structure wherein a piston and an air-filled chamber having deformable walls are permitted to move relative to one another to damp relative movement as the walls of the air-filled chamber roll along the outside surface of the piston.
It is an object of the patent invention to provide a pneumatic air spring with vibration damping characteristics of a viscous damping nature which are damping characteristics beyond the normal structural damping characteristics of the above mentioned class of air spring. Structural damping is that damping caused by frictional forces produced between the molecules of a seemingly elastic body being flexed whereas viscous damping is caused by fluid friction and is characterized by the fact that the friction force is proportional to the speed of the moving body.
Another object of the present invention is to provide such a spring which effectively cushions vibrations through a broad range of vibration frequencies.
Still another object of the present invention is to provide such a spring whose spring rate characteristics during operation do not depend upon any mechanical adjustment or an active valve system.
Yet another object of the present invention is to provide such a spring which evidences a low spring rate when exposed to vibrations of low frequency yet evidences a higher, or more aggressive, spring rate when exposed to vibrations of high frequency and longer amplitude.
A further object of the present invention is to provide such a spring which when used for damping vibrations of a vehicle seat provides an occupant of the seat with enhanced ride comfort and helps to maintain the movement of the seat within a desirable range of seat travel.
A still further object of the present invention is to provide such a spring which, upon exposure to a shock of high frequency and high amplitude, returns to its equilibrium position with minimum oscillation.
A yet further object of the present invention is to provide such a spring of uncomplicated construction which decreases its unloading rate by effectively dissipating the energy from the loading cycle without active mechanism or frictional device.
One more object of the present invention is to provide a vehicle seat assembly within which such a spring is incorporated.